The present invention relates to an optical coupling device used for transmitting optical signals between a number of stationary terminal units and a movable element in which the number of stationary terminals units coupled through the optical fibers of an optical cable to the movable element can be increased as required.
Where signals are transmitted through a multi-core optical cable between a seabed sensor and a measuring instrument or a control unit on a ship, in playing out the optical cable connected between the seabed sensor and the measuring instrument or the control unit, it is necessary to vary the length of cable played out depending on the depth of water. Therefore, it is necessary that the optical cable container be so designed that the optical cable can be readily played out and wound in and the space occupied by the container be small. Accordingly, usually the optical cable is wound on a drum. However, in this case a problem arises in that it is rather difficult to satisfactorily couple the optical cable (including optical fibers) wound on the rotating drum to the measuring instrument or the control unit which are relatively stationary. In addition to this problem, there are inherent difficulties involved in connecting the optical fibers of the multi-core optical cable.
An example of a conventional optical coupling device is shown in FIGS. 1 and 2. A two-core optical cable 12 is wound on a rotor 1 such as a drum. One end of the optical cable 2 is connected to a seabed sensor 3 while the other end of the optical cable 2 wound on the rotor 1 is inserted into a through-hole 1a formed in the winding barrel of the rotor 1. The rotor 1 is hollow. Hollow rotating shafts 4 extend from both ends of the hollow rotor 1. A rotary joint 5 is provided at the end of each rotating shaft 4. The rotary joint 5 includes the end portion of the rotating shaft 4 and a closed-end cylinder 7 which is fixedly secured to a stationary frame 6. The optical cable 2 inserted into the through-hole is branched into two optical fibers 2a inside the hollow rotor 1. The two optical fibers 2a pass through the rotating shafts 4 and are positioned at the ends of the rotating shafts 4 along the axes of the latter. One end of an optical fiber 9 is connected to a stationary terminal unit 8 and the other end is positioned on the axis of the cylinder 7 at the joint 5 on each side of the rotor 1. The optical fibers 9 are suitably coupled to the optical fibers 2a for signal transmission as the end portions of the rotating shafts 5 are maintained in axial alignment with the cylinders 7 in such a manner that the shafts are slightly spaced from or in contact with the cylinders. In FIGS. 1 and 2 reference numeral 10 designates bearings supporting the rotor 1.
The arrangement of the optical coupling device shown in FIGS. 1 and 2 is applicable to a two-core optical cable. However, it cannot be used with optical cables having more than two cores because the ends of corresponding fibers cannot then be kept in alignment.
The invention further relates to a device for transmitting electric signals, electric power or optical signals between an externally and stationarily disposed electrical device or optical device and an electric wire or optical cable wound on a rotary drum through a lead wire or cable without using a rotary slide contactor.
FIG. 3 shows a conventional system of this type, in which electrical signals or the like are transmitted through a cable 102 wound on a drum between a movable electric unit 103 connected to the cable 102 and a main electric device 104 which is provided separately from the drum 101 while the cable 102 is played out or wound on the drum 102. In this case, generally a rotary slide contactor 105 such as a slip ring is interposed between the cable 102 on the rotating drum 101 and the stationary main electric device 104 so as to transmit electrical signals between the movable electric unit 102 and the main electric device 104.
However, the conventional system is disadvantageous in that the provision of the rotary slide contactor may generate noise, increase the circuit resistance, and make the electrical characteristics non-uniform. That is, it may result in various circuit losses. Accordingly, the conventional system is especially not suitable for high frequency signal transmission and it requires the provision of a special coupling system for optical communication.
In FIG. 3, reference numeral 106 designates a lead cable connecting the main electric device and the slide contactor, 107 a drum driving motor, and 108 a drum drive transmission device.